The present invention relates to a reading apparatus for reading the shape or position of a recess or projection of a target object having a fine recess or projection such as a valley or ridge of a fingertip.
A structure described in Jpn. Pat. Appln. KOKAI Publication No. 6-325158 is conventionally known as a reading apparatus for reading the shapes or positions of fine recesses or projections such as valleys or ridges of a fingertip. As shown in FIG. 16, this apparatus has a two-dimensional photosensor 2 disposed on a surface of a light source or an illuminant 1. An optical fiber bundle plate 3 having a bundle of a plurality of optical fibers 3a is formed on the two-dimensional photosensor 2. A light-reflecting plate 4 is disposed on the optical fiber bundle plate 3. The two-dimensional photosensor 2 has a light-shielding plate 2c having an openings 2b on a transparent substrate 2a. Sensor portions 2d are formed on the light-shielding plate 2c. The light-reflecting plate 4 is made of a transparent material sheet and has a plurality of V-grooves 4b on each of which a light-reflecting-layer 4a made of an aluminum or the like is deposited. A portion between the two adjacent V-grooves 4b is constituted by a projection 4d having a flat upper surface 4c and a substantially trapezoidal section.
Almost all the components of this reading apparatus are flat to obtain a low-profile structure. As indicated by arrows in FIG. 16, parallel light beams are emitted vertically from the upper surface of the surface illuminant 1 and transmitted to the upper surfaces 4c of the light-reflecting plate 4 through the openings 2b of the two-dimensional photosensor 2 and optical fibers 3a of the optical fiber bundle plate 3. The transmitted light beams are reflected by the light-reflecting layers 4a on the V-grooves 4b of the light-reflecting plate 4. These reflected light beams come into the adjacent optical fibers 3a other than the light-transmitting portion (optical fiber 3a) of the optical fiber bundle plate 3 and are incident on the sensor portions 2d of the two-dimensional photosensor 2. In this case, the beams are reflected by the upper surfaces 4c of the projections 4d of the light-reflecting plate 4 which correspond to the recesses (valleys) of the fingertip, and the beams are absorbed at the upper surfaces 4c which contact to the projections (ridges) of the fingertip. Therefore, an image having bright and dark portions optically emphasized in correspondence with the recesses and projections of the fingertip, thereby reading the fingerprint.
In the conventional reading apparatus of this type, the parallel beams are emitted vertically from the upper surface of the surface illuminant 1 and transmitted to the upper surface of the light-reflecting plate 4 through the openings 2b of the two-dimensional photosensor 2 and the optical fibers 3a of the optical fiber bundle plate 3. The light beams reflected by the upper surfaces 4c of the projections 4d of the light-reflecting plate 4 are reflected by the light-reflecting layer 4a of the V-grooves 4b of the light-reflecting plate 4 and come into the adjacent optical fibers 3a other than the optical fiber 3a having undergone transmission. The incident angle at the optical fiber 3a having a small light reception angle increases to result in a large loss. This makes it difficult to obtain a sufficiently high contrast. In addition, to make the light beams reflected by the upper surfaces 4c of the projections 4d of the light-reflecting plate 4 come into the optical fibers 3a of the optical fiber bundle plate 3 which are located at the predetermined positions and strike the sensor portions 2d of the two-dimensional photosensor 2 which are located at the predetermined positions in a prescribed manner, the projections 4d of the light-reflecting plate 4, the optical fibers 3a of the optical fiber bundle plate 3, and the sensor portions 2d of the two-dimensional photosensor 2 must be accurately positioned in a one-to-one correspondence, resulting in a low productivity and a high cost.